Hydrocarbon dehydrogenation with a superactive multimetallic catalytic composite for use therein

ABSTRACT

Dehydrogenatable hydrocarbons are dehydrogenated by contacting them, at hydrocarbon dehydrogenation conditions, with a novel superactive multimetallic catalytic composite comprising a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of a catalytically effective amount of a platinum group component maintained in the elemental metallic state. An example of the superactive nonacidic multimetallic catalytic composite disclosed herein is a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of catalytically effective amounts of an alkali or alkaline earth component and of a platinum group component which is maintained in the elemental metallic state during the incorporation of the rhenium carbonyl component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my prior, copendingapplication Ser. No. 907,240 filed May 18, 1978 and issued as U.S. Pat.No. 4,157,989 on June 12, 1979, which in turn is a division of my prior,copending application Ser. No. 833,332 filed Sept. 14, 1977 and issuedas U.S. Pat. No. 4,165,276 on June 12, 1979. All of the teachings ofthese prior applications are specifically incorporated herein byreference.

The subject of the present invention is, broadly, an improved method fordehydrogenating a dehyodrogenatable hydrocarbon to produce a hydrocarbonproduct containing the same number of carbon atoms but fewer hydrogenatoms. In another aspect, the present invention involves a method ofdehydrogenating normal paraffin hydrocarbons containing 3 to 30 carbonatoms per molecule to the corresponding normal mono-olefin with minimumproduction of side products. In yet another aspect, the presentinvention relates to a novel superactive nonacidic multimetalliccatalytic composite comprising a combination of a catalyticallyeffective amount of a pyrolyzed rhenium carbonyl component with a porouscarrier material containing a uniform dispersion of catalyticallyeffective amounts of an alkali or alkaline earth component and aplatinum group component which is maintained in the elemental state.This nonacidic composite has highly beneficial characteristics ofactivity, selectivity, and stability when it is employed in thedehydrogenation of dehydrogenatable hydrocarbons such as aliphatichydrocarbons, naphthene hydrocarbons, and alkylaromatic hydrocarbons.

The conception of the present invention followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking function, and superior conversion,selectivity, and stability characteristics when employed in hydrocarbonconversion processes that have traditionally utilized dual-functioncatalytic composites. In my prior application Ser. No. 833,332, Idisclosed a significant finding with respect to a multimetalliccatalytic composite meeting these requirements. More specifically, Idetermined that a pyrolyzed rhenium carbonyl component can be utilized,under certain specified conditions, to beneficially interact with theplatinum group component of a dual-function catalyst with a resultingmarked improvement in the performance of such a catalyst. Now I haveascertained that a catalytic composite, comprising a combination ofcatalytically effective amounts of a platinum group component and of apyrolyzed rhenium carbonyl component with a porous carrier material canhave superior activity, selectivity and stability characteristics whenit is employed in a hydrocarbon dehydrogenation process if thesecomponents are uniformly dispersed in the porous carrier material in theamounts specified hereinafter and if the oxidation state of the platinumgroup component is carefully controlled so that substantially all ofthis component is present in the elemental metallic state during theincorporation of the rhenium carbonyl component. I have discerned,moreover, that a particularly preferred multimetallic catalyticcomposite of this type contains not only a platinum group component, anda pyrolyzed rhenium carbonyl component, but also an alkali or alkalineearth component in an amount sufficient to ensure that the resultingcatalyst is nonacidic.

The dehydrogenation of dehydrogenatable hydrocarbons is an importantcommercial process because of the great and expanding demand fordehydrogenated hydrocarbons for use in the manufacture of variouschemical products such as detergents, plastics, synthetic rubbers,pharmaceutical products, high octane gasolines, perfumes, drying oils,ion-exchange resins, and various other products well known to thoseskilled in the art. One example of this demand is in the manufacture ofhigh octane gasoline by using C₃ and C₄ mono-olefins to alkylateisobutane. Another example of this demand is in the area ofdehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins having 4 to 30 carbon atoms per molecule. These normalmono-olefins can, in turn, be utilized in the synthesis of a vast numberof other chemical products. For example, derivatives of normalmono-olefins have become of substantial importance to the detergentindustry where they are utilized to alkylate an aromatic, such asbenzene, with subsequent transformation of the product arylalkane into awide variety of biodegradable detergents such as the alkylaryl sulfonatetypes of detergents which are most widely used today for household,industrial, and commercial purposes. Still another large class ofdetergents produced from these normal mono-olefins are the oxyalkylatedphenol derivatives in which the alkylphenol base is prepared by thealkylation of phenol with these normal mono-olefins. Still another typeof detergent produced from these normal mono-olefins are thebiodegradable alkylsulfonates formed by the direct sulfation of thenormal mono-olefins. Likewise, the olefin can be subjected to directsulfonation with sodium bisulfite to make biodegradable alkylsulfonates.As a further example, these mono-olefins can be hydrated to producealcohols which then, in turn, can be used to produce plasticizers and/orsynthetic lube oils.

Regarding the use of products made by the dehydrogenation ofalkylaromatic hydrocarbons, they find wide application in the petroleum,petrochemical, pharmaceutical, detergent, plastic, and the likeindustries. For example, ethylebenzene is dehydrogenated to producestyrene which is utilized in the manufacture of polystyrene plastics,styrene-butadiene rubber, and the like products. Isopropylbenzene isdehydrogenated to form alpha-methylstyrene which, in turn, isextensively used in polymer formation and in the manufacture of dryingoils, ion-exchange resins, and the like materials.

Responsive to this demand for these dehydrogenation products, the arthas developed a number of alternative methods to produce them incommercial quantities. One method that is widely utilized involves theselective dehydrogenation of a dehydrogenatable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst at dehydrogenationconditions. As is the case with most catalytic procedures, the principalmeasure of effectiveness for this dehydrogenation method involves theability to perform its intended function with minimum interference ofside reactions for extended periods of time. The analytical terms usedin the art to broadly measure how well a particular catalyst performsits intended functions in a particular hydrocarbon conversion reactionare activity, selectivity, and stability, and for purposes of discussionhere, these terms are generally defined for a given reactant as follows:(1) activity is a measure of the catalyst's ability to convert thehydrocarbon reactant into products at a specified severity level whereseverity level means the specific reaction conditions used--that is, thetemperature, pressure, contact time, and presence of diluents such as H₂; (2) selectivity usually refers to the amount of desired product orproducts obtained relative to the amount of the reactant charged orconverted; (3) stability refers to the rate of change with time of theactivity and selectivity parameters--obviously, the smaller rateimplying the more stable catalyst. In a dehydrogenation process, morespecifically, activity commonly refers to the amount of conversion thattakes place for a given dehydrogenatable hydrocarbon at a specifiedseverity level and is typically measured on the basis of disappearanceof the dehydrogenatable hydrocarbon; selectivity is typically measuredby the amount, calculated on a mole or weight percent of converteddehydrogenatable hydrocarbon basis, of the desired dehydrogenatedhydrocarbon obtained at the particular activity or severity level; andstability is typically equated to the rate of change with time ofactivity as measured by disappearance of the dehydrogenatablehydrocarbon and of selectivity as measured by the amount of desireddehydrogenated hydrocarbon produced. Accordingly, the major problemfacing workers in the hydrocarbon dehydrogenation art is the developmentof a more active and selective catalytic composite that has goodstability characteristics.

I have now found a superactive multimetallic catalytic composite whichpossesses improved activity, selectivity, and stability when it isemployed in a process for the dehydrogenation of dehydrogentablehydrocarbons. In particular, I have determined that the use of asuperactive multimetallic catalyst, comprising a combination ofcatalytically effective amounts of a platinum group component and apyrolyzed rhenium carbonyl component with a porous refractory carriermaterial, can enable the performance of a hydrocarbon dehydrogenationprocess to be substantially improved if the platinum group component isuniformly dispersed throughout the carrier material prior toincorporation of the rhenium carbonyl component, if the oxidation stateof the platinum group component is maintained in the elemental metallicstate prior to and during contact with the rhenium carbonyl componentand if high temperature treatments in the presence of oxygen and/orwater of the reaction product of the rhenium carbonyl with the carriermaterial containing the platinum group component is avoided. Moreover,particularly good results are obtained when this composite is combinedwith an amount of an alkali or alkaline earth component sufficient toensure that the resulting catalyst is nonacidic and utilized to producedehydrogenated hydrocarbons containing the same carbon structure as thereactant hydrocarbon but fewer hydroben atoms. This nonacidic compositeis particularly useful in the dehydrgenation of long chain normalparaffins to produce the corresponding normal mono-olefin withminimization of side reactions such as skeletal isomerization,aromatization, cracking and polyolefin formation. In sum, the presentinvention involves the significant finding that a pyrolyzed rheniumcarbonyl component can be utilized under the circumstances specifiedherein to beneficially interact with and promote a hydrocarbondehydrogenation catalyst containing a platinum group metal.

It is, accordingly, one object of the present invention to provide anovel method for the dehydrogenation of dehydrogenatable hydrocarbonsutilizing a superactive multimetallic catalytic composite comprisingcatalytically effective amounts of a platinum group component, and apyrolyzed rhenium carbonyl component combined with a porous carriermaterial. A second object is to provide a novel nonacidic catalyticcomposite having superior performance characteristics when utilized in ahydrocarbon dehydrogenation process. Another object is to provide animproved method for the dehydrogenation of normal paraffin hydrocarbonsto produce normal mono-olefins which method minimizes undesirable sidereactions such as cracking, skeletal isomerization, polyolefinformation, disproportionation and aromatization.

In brief summary, one embodiment of the present invention involves amethod for dehydrogenating a dehydrogenatable hydrocarbon which compriescontacting the hydrocarbon at hydrocarbon dehydrogenation conditionswith a superactive multimetallic catalytic composite comprising a porouscarrier material containing a uniform dispersion of catalyticallyeffective and available amounts of a platinum group component and of apyrolyzed rhenium carbonyl component. Substantially all of the platinumgroup component is, moreover, present in the composite in the elementalmetallic state during the incorporation of the rhenium carbonylcomponent and the pyrolysis of the rhenium carbonyl component isperformed after it has been reacted with the porous carrier materialcontaining the platinum group component. Further, these components arepreferably present in this composite in amounts, calculated on anelemental basis, sufficient to result in the composite containing about0.01 to about 2 wt. % platinum group metal, and about 0.01 to about 5wt. % rhenium derived from the rhenium carbonyl component, and thiscomposite is preferably maintained in a substantially halogen-free stateduring use in the dehydrogenation method.

A second embodiment relates to the dehydrogenation method described inthe first embodiment wherein the dehydrogenatable hydrocarbon is analiphatic compound containing 2 to 30 carbon atoms per molecule.

A third embodiment comprehends a superactive nonacidic catalyticcomposite comprising a porous carrier material having uniformlydispersed therein catalytically effective and available amounts of aplatinum group component, a pyrolyzed rhenium carbonyl component, and analkali or alkaline earth component. These components are preferablypresent in amounts sufficient to result in the catalytic compositecontaining, on an elemental basis, about 0.01 to about 2 wt. % platinumgroup metal, about 0.1 to about 5 wt. % of the alkali metal or alkalineearth metal and about 0.01 to about 5 wt. % rhenium, derived from therhenium carbonyl component. In addition, substantially all of theplatinum group component is present in the elemental metallic stateduring incorporation of the rhenium carbonyl component, the pyrolysis ofthe rhenium carbonyl component occurs after combustion thereof with theporous carrier material containing the platinum group component andsubstantially all of the alkali or alkaline earth component is presentin an oxidation state above that of the elemental metal.

Another embodiment pertains to a method for dehydrogenating adehydrogenatable hydrocarbon which comprises contacting the hydrocarbonwith the nonacidic catalytic composite described in the third embodimentat dehydrogenation conditions.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrogenatable hydrocarbons, operatingconditions for use in the dehydrogenation process, and the likeparticulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention. It is to beunderstood that (1) the term "nonacidic" means that the catalystproduces less than 10% conversion of 1-butene to isobutylene when testedat dehydrogenation conditions and, preferably, less than 1%; (2) theexpression "uniformly dispersed throughout a carrier material" isintended to mean that the amount of the subject component, expressed ona weight percent basis, is approximately the same in any reasonablydivisible portion of the carrier material as it is in gross; and (3) theterm "substantially halogen-free" means that the total amount of halogenpresent in the catalytic composite in any form is less than about 0.2wt. %, calculated on an elemental basis.

Regarding the dehydrogenatable hydrocarbon that is subjected to themethod of the present invention, it can, in general, be an organiccompound having 2 to 30 carbon atoms per molecule and containing atleast one pair of adjacent carbon atoms having hydrogen attachedthereto. That is, it is intended to include within the scope of thepresent invention, the dehydrogenation of any organic compound capableof being dehydrogenated to produce products containing the same numberof carbon atoms but fewer hydrogen atoms, and capable of being vaporizedat the dehydrogenation temperatures used herein. More particularly,suitable dehydrogenatable hydrocarbons are: aliphatic hydrocarbonscontaining 2 to 30 carbon atoms per molecule, alkylaromatic hydrocarbonswhere the alkyl group contains 2 to 6 carbon atoms, and naphthenes oralkyl-substituted naphthenes. Specific examples of suitabledehydrogenatable hydrocarbons are: (1) alkanes such as ethane, propane,n-butane, isobutane, n-pentane, isopentane, n-hexane, 2-methylpentane,3-methypenetane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,2,2,3-trimethylbutane, and the like compounds; (2) naphthenes such ascyclopentane, cyclohexane, methylcyclopentane, ethylcyclopentane,n-propylcyclopentane, 1,3-dimethylcyclohexane, and the like compounds;and (3) alkylaromatics such as ethylbenzene, n-butylbenzene,1,3,5-triethylbenzene, isopropylbenzene, isobutylbenzene,ethylnaphthalene, and the like compounds.

In a preferred embodiment, the dehydrogenatable hydrocarbon is a normalparaffin hydrocarbon having about 3 to 30 carbon atoms per molecule. Forexample, normal paraffin hydrocarbons containing about 10 to 18 carbonatoms per molecule are dehydrogenated by the subject method to producethe corresponding normal mono-olefin which can, in turn, be allylatedwith benzene and sulfonated to make alkybenzene sulfonate detergentshaving superior biogradability. Likewise, n-alkanes having 10 to 18carbon atoms per molecule can be dehydrogenated to the correspondingnormal mono-olefin which, in turn, can be sulfonated or sulfated to makeexcellent detergents. Similarly, n-alkanes having 6 to 10 carbon atomscan be dehydrogenated to form the corresponding mono-olefin which can,in turn, be hydrated to produce valuable alcohols. Preferred feedstreams for the manufacture of detergent intermediates contain a mixtureof 4 or 5 adjacent normal paraffin homologues such as C₁₀ to C₁₃, C₁₁ toC₁₄, C₁₁ to C₁₅ and the like mixtures. In an especially preferredembodiment, charge stock to present method is substantially purepropane.

The superactive multimetallic catalyst used in the present inventioncomprises a porous carrier material or support having combined therewitha uniform dispersion of catalytically effective amounts of a platinumgroup component, a pyrolyzed rhenium carbonyl component, and, in thepreferred case, an alkali or alkaline earth component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon dehydrogenation process, andit is intended to include within the scope of the present inventioncarrier materials which have traditionally been utilized indual-function hydrocarbon conversion catalysts such as: (1) activatedcarbon, coke, or charcoal; (2) silica or silica gel, silicon carbide,clays, and silicates including those synthetically prepared andnaturally occurring, which may or may not be acid treated, for example,attapulgus clay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, procelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, CaAl₂ O₄, and other like compounds having the formulaMO-Al₂ O₃ where M is a metal having a valence of 2; and (7) combinationsof elements from one or more of these groups. The preferred porouscarrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas gamma-, eta-, and theta-alumina, with gamma- or eta-alumina givingbest results. In addition, in some embodiments the alumina carriermaterial may contain minor proportions of other well known refractoryinorganic oxides such as silica, zirconia, magnesia, etc.; however, thepreferred support is substantially pure gamma- or eta-alumina. Preferredcarrier materials having an apparent bulk density of about 0.3 to about0.8 g/cc and surface area characteristics such that the average porediameter is about 20 to 300 Angstroms (B.E.T.), the pore volume is about0.1 to about 1 cc/g (B.E.T.) and the surface area is about 100 to about500 m² /g (B.E.T.). In general, best results are typically obtained witha substantially halogen-free gamma-alumina carrier material which isused in the form of spherical particles having a relatively smalldiameter (i.e. typically about 1/16 inch), an apparent bulk density ofabout 0.2 to about 0.8 g/cc, a pore volume of about 0.3 to about 0.8cc/g (B.E.T.), and a surface area of about 125 to about 250 m² /g(B.E.T.).

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere, and alumina spheres may becontinuously manufactured by the well known oil drop which comprises:forming an alumina hydrosol by any of the techniques taught in the artand preferably by reacting aluminum metal with hydrochloric acid,combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° F.to about 400° F. and subjected to a calcination procedure at atemperature of about 850° F. to about 1300°0 F. for a period of about 1to about 20 hours. It is a good practice to subject the calcinedparticles to a high temperature treatment with steam in order to removeundesired acidic components such as residual chlorine and therebyprepare the preferred substantially halogen-free carrier material. Thispreparation procedure effects conversion of the alumina hydrogel to thecorresponding crystalline gamma-alumina. See the teachings of U.S. Pat.No. 2,620,314 for additional details.

Another particularly preferred alumina carrier material is synthesizedfrom a unique crystalline alumina powder which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a by-product from a Zieglerhigher alcohol synthesis reaction as described in Zeigler's U.S. Pat.No. 2,892, 858. For purposes of simplification, the name "Ziegleralumina" is used herein to identify this material. It is presentlyavailable from the Conoco Chemical Division of Continental Oil Companyunder the trademark Catapal. This material is an extremely high purityalpha-alumina monohydrate (boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina. It iscommercially available in three forms: (1) Catapal SB--a spray driedpowder having a typical surface area of 250 m² /g; (2) Catapal NG-- arotary kiln dried alumina having a typical surface area of 180 m² /g;and (3) Dispal M--a finely divided dispersable product having a typicalsurface area of about 185 m² /g. For purposes of the present invention,the preferred starting material is the spray dried powder, Catapal SB.Thia alpha-alumina monohydrate powder may be formed into a suitablecatalyst material according to any of the techniques known to thoseskilled in the catalyst carrier material forming art. Spherical carriermaterial particles can be formed, for example, from this Ziegler aluminaby: (1) converting the alpha-alumina monohydrate powder into an aluminasol by reaction with a suitable peptizing acid and water and thereafterdropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are easilyconverted to a gamma-alumina carrier material by known methods; (2)forming an extrudate from the powder by established methods andthereafter rolling the extrudate particles on a spinning disc untilspherical particles are formed which can then be dried and calcined toform the desired particles of spherical carrier material; and (3)wetting the powder with a suitable peptizing agent and thereafterrolling particles of the powder into spherical masses of the desiredsize in much the same way that children have been known to make parts ofsnowmen by rolling snowballs down hills covered with wet snow. Thisalumina powder can also be formed in any other desired shape or type ofcarrier material known to those skilled in the art such as rods, pills,pellets, tablets, granules, extrudates and the like forms by methodswell known to the practitioners of the catalyst carrier material formingart. The preferred type of carrier material for the present invention isa cylindrical extrudate having a diameter of about 1/32" to about 1/8"(especially about 1/16") and a length to diameter (L/D) ratio of about1:1 to about 5:1, with a L/D ratio of about 2:1 being especiallypreferred. The especially preferred extrudate form of the carriermaterial is preferably prepared by mixing the alumina powder with waterand a suitable peptizing agent such as nitric acid, acetic acid,aluminum nitrate and the like material until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss of ignition (LOI) at 500° C. of about 45 to 65wt. %, with a value of about 55 wt. % being especially preferred. On theother hand, the acid addition rate is generally sufficient to provideabout 2 to 7 wt. % of the volatile free alumina powder used in the mix,with a value of about 3 to 4% being especially preferred. The resultingdough is then extruded through a suitably sized die to form extrudateparticles. It is to be noted that it is within the scope of the presentinvention to treat the resulting dough with an aqueous alkaline reagentsuch as an aqueous solution of ammonium hydroxide in accordance with theteachings of U.S. Pat. No. 3,661,805. This treatment may be performedeither before or after extrusion, with the former being preferred. Theseparticles are then dried at a temperature of about 500° to 800° F. for aperiod of about 0.1 to about 5 hours and thereafter calcined at atemperature of about 900° F. to about 1500° F. for a period of about 0.5to about 5 hours to form the preferred extrudate particles of theZiegler alumina carrier material. In addition, in some embodiments ofthe present invention the Ziegler alumina carrier material may containminor proportions of other well known refractory inorganic oxides suchas silica, titanium dioxide, zirconium dioxide, chromium oxide,beryllium oxide, vanadium oxide, cesium oxide, hafnium oxide, zincoxide, iron oxide, cobalt oxide, magnesia, boria, thoria, and the likematerials which can be blended into the extrudable dough prior to theextrusion of same. In the same manner crystalline zeoliticaluminosilicates such as naturally occurring or synthetically preparedmordenite and/or faujasite, either in the hydrogen form or in a formwhich has been treated with a multivalent cation, such as a rare earth,can be incorporated into this carrier material by blending finelydivided particles of same into the extrudable dough prior to extrusionof same. A preferred carrier material of this type is a substantiallyhalogen-free and substantially pure Ziegler alumina having an apparentbulk density (ABD) of about 0.4 to 1 g/cc (especially an ABD of about0.5 to about 0.85 g/cc), a surface area (B.E.T.) of about 150 to about280 m² /g (preferably about 185 to about 235 m² /g) and a pore volume(B.E.T.) of about 0.3 to about 0.8 cc/g.

A first essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as afirst component of the superactive catalytic composite. It is anessential feature of the present invention that substantially all ofthis platinum group component is uniformly dispersed throughout theporous carrier material in the elemental metallic state prior to theincorporation of the rhenium carbonyl ingredient. Generally, the amountof this component present in the form of catalytic composites is smalland typically will comprise about 0.01 to about 2 wt. % of finalcatalytic composite, calculated on an elemental basis. Excellent resultsare obtained when the catalyst contains about 0.05 to about 1 wt. % ofplatinum, iridium, rhodium or palladium metal. Particularly preferredmixtures of these platinum group metals preferred for use in thecomposite of the present invention are: (1) platinum and iridium and (2)platinum and rhodium.

This platinum group component may be incorporated in the porous carriermaterial in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion-exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiamino-platinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of a platinum, iridium, rhodium,or palladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is ordinarilypreferred. Nitric acid or the like acid is also generally added to theimpregnation solution in order to further facilitate the uniformdistribution of the metallic components throughout the carrier material.In addition, it is generally preferred to impregnate the carriermaterial after it has been calcined in order to minimize the risk ofwashing away the valuable platinum group component.

A highly preferred optional ingredient of the catalyst used in thepresent invention is the alkali or alkaline earth component. Morespecifically, this component is selected from the group consisting ofthe compounds of the alkali metals--cesium, rubidium, potassium, sodium,and lithium--and of the alkaline earth metals--calcium, strontium,barium, and magnesium. This component exists within the catalyticcomposite in an oxidation state above that of the elemental metal suchas a relatively stable compound such as the oxide of hydroxide, or incombination with one or more of the other components of the composite,or in combination with the carrier material such as, for example, in theform of an alkali or alkaline earth metal aluminate. Since, as isexplained hereinafter, the composite containing the alkali or alkalineearth component is always calcined or oxidized in an air atmospherebefore use in the dehydrogenation of hydrocarbons, the most likely statethis component exists in during use in the dehydrogenation reaction isthe corresponding metallic oxide such as lithium oxide, potassium oxide,sodium oxide, and the like. Regardless of what precise form in which itexists in the composite, the amount of this component utilized ispreferably selected to provide a nonacidic composite containing about0.1 to about 5 wt. % of the alkali metal or alkaline earth metal, and,more preferably, about 0.25 to about 3.5 wt. %. Best results areobtained when this component is a compound of lithium or potassium. Thefunction of this component is to neutralize any of the acidic materialsuch as halogen which may have been used in the preparation of thepresent catalyst so that the final catalyst is nonacidic.

This alkali or alkaline earth component may be combined with the porouscarrier material in any manner known to those skilled in the art toresult in a relatively uniform dispersion of this component throughoutthe carrier material with consequential neutralization of any acidicsites which may be present therein. Typically good results are obtainedwhen it is combined by impregnation, coprecipitation, ion-exchange, andthe like procedures. The preferred procedure, however, involvesimpregnation of the carrier material either before, during or after itis calcined, or before, during, or after the other metallic ingredientsare added to the carrier material. Best results are ordinarily obtainedwhen this component is added to the carrier material simultaneously withor after the platinum group component and before the rhenium carbonylcomponent because the alkali metal or alkaline earth metal componentacts to neutralize the acidic materials used in the preferredimpregnation procedure for the platinum group component. In fact, it ispreferred to add the platinum group and alkali or alkaline earthcomponents to the carrier material, oxidize the resulting composite in awet air stream at a high temperature (i.e. typically about 600° to 1000°F.), then treat the resulting oxidized composite with steam or a mixtureof air and steam at a relatively high temperature of about 600° to about1050° F. in order to remove at least a portion of any residual acidityand thereafter add the rhenium carbonyl component. Typically, theimpregnation of the carrier material with this component is performed bycontacting the carrier material with a solution of a suitabledecomposable compound or salt of the desired alkali or alkaline earthmetal. Hence, suitable compounds include the alkali or alkaline earthmetal halides, nitrates, acetates, carbonates, phosphates, and the likecompounds. For example, excellent results are obtained by impregnatingthe carrier material with an aqueous solution of chloroplatinic acid,lithium nitrate or potassium nitrate and nitric acid. Ordinarily, theamount of alkali or alkaline earth component is selected to produce acomposite having an atomic ratio of alkali metal or alkaline earth metalto platinum group metal of about 5:1 to about 100:1 or more, with thepreferred range being about 10:1 to about 75:1.

After the platinum group component and the optional alkali or alkalineearth component are combined with the porous carrier material, theresulting metals-containing carrier material will generally be dried ata temperature of about 200° F. to about 600° F. for a period oftypically about 1 to about 24 hours or more and thereafter oxidized at atemperature of about 600° F. to about 1000° F. in an air or oxygenatmosphere for a period of about 0.5 to about 10 or more hours effectiveto convert substantially all of the platinum group and the alkali oralkaline earth components to the corresponding oxide forms. When acidicmaterials are used in incorporating these metallic components, bestresults are ordinarily achieved when the resulting oxidized composite issubjected to a high temperature treatment with steam or with a mixtureof steam and a diluent gas such as air or nitrogen either during orafter this oxidation step in order to remove as much as possible of theundesired acidic components such as halogen and thereby prepare asubstantially halogen-free, metals-containing oxidized carrier material.It is to be noted that it is essential that conditions used in thisacidic component stripping step be very carefully chosen to avoid anypossibility of sintering or agglomerating the platinum group component.

A critical feature of the present invention involves subjecting theresulting oxidized, platinum group metal-containing, and typicallyalkali or alkaline earth metal-containing carrier material to asubstantially water-free reduction step before the incorporation of therhenium component by means of the rhenium carbonyl reagent. Theimportance of this reduction step comes from my observation that when anattempt is made to prepare the instant catalytic composite without firstreducing the platinum group component, no significant improvement in theplatinum-rhenium catalyst system is obtained; put another way, it is myfinding that it is essential for the platinum group component to be welldispersed in the porous carrier material in the elemental metallic stateprior to incorporation of the rhenium component by the unique procedureof the present invention in order for synergistic interaction of therhenium carbonyl with the dispersed platinum group metal to occuraccording to the theories that I have previously explained in my priorapplication Ser. No. 833,332. Accordingly, this reduction step isdesigned to reduce subsantially all of the platinum group component tothe elemental metallic state and to assure a relatively uniform andfinely divided dispersion of this metallic component throughout theporous carrier material. Preferably, a substantially pure and dryhydrogen-containing stream (by the use of the word "dry" I means that itcontains less than 20 vol. ppm. water and preferably less than 5 vol.ppm. water) is used as the reducing agent in this step. The reducingagent is contacted with the oxidized, platinum group metal-containingcarrier material at conditions including a reduction temperature ofabout 450° F. to about 1200° F. for a period of about 0.5 to about 10 ormore hours selected to reduce substantially all of the platinum groupcomponent to the elemental metallic state. Once this condition of finelydivided dispersed platinum group metal in the porous carrier material isachieved, it is important that environments and/or conditions that coulddisturb or change this condition be avoided; specifically, I much preferto maintain the freshly reduced carrier material containing the platinumgroup metal under a blanket of inert gas to avoid any possibility ofcontamination of same either by water or by oxygen.

A second essential ingredient of the present superactive catalyticcomposite is a rhenium component which I have chosen to characterize asa pyrolyzed rhenium carbonyl component in order to emphasize that therhenium moiety of interest in my invention is the rhenium produced bydecomposing a rhenium carbonyl in the presence of a finely divideddispersion of a platinum group metal and in the absence of materialssuch as oxygen or water which could interfere with the desiredinteraction of the rhenium carbonyl component with the platinum groupmetal component. In view of the fact that all of the rhenium containedin a rhenium carbonyl compound is present in the elemental metallicstate, an essential requirement of my invention is that the resultingreaction product of the rhenium carbonyl compound or complex with theplatinum group metal-loaded carrier material is not subjected toconditions which could in any way interfere with the maintenance of therhenium moiety in the elemental metallic state; consequently, avoidanceof any conditions which would tend to cause the oxidation of any portionof the rhenium ingredient or of the platinum group ingredient is arequirement for full realization of the synergistic interaction enabledby the present invention. This rhenium component may be utilized in theresulting composite in any amount that is catalytically effective withthe preferred amount typically corresponding to about 0.01 to about 5wt. % thereof, calculated on an elemental rhenium basis. Best resultsare ordinarily obtained with about 0.05 to about 1 wt. % rhenium. Thetraditional rule for rhenium-platinum catalyst system is that bestresults are achieved when the amount of the rhenium component is set asa function of the amount of the platinum group component also hold formy composition; specifically, I find that best results with a rhenium toplatinum group metal atomic ratio of about 0.1:1 to about 10:1, with anespecially useful range comprising about 0.2:1 to about 5:1 and withsuperior results achieved at an atomic ratio of rhenium to platinumgroup metal of about 1:1.

The rhenium carbonyl ingredient may be reacted with the reduced platinumgroup metal-containing porous carrier material in any suitable mannerknown to those skilled in the catalyst formulation art which results inrelatively good contact between the rhenium carbonyl complex and theplatinum group component contained in the porous carrier material. Oneacceptable procedure for incorporating the rhenium carbonyl compoundinto the composite involves sublimating the rhenium carbonyl complexunder conditions which enable it to pass into the vapor phase withoutbeing decomposed and thereafter contacting the resulting rheniumcarbonyl sublimate with the platinum group metal-containing porouscarrier material under conditions designed to achieve intimate contactof the carbonyl reagent with the platinum group metal dispersed on thecarrier material. Typically, this procedure is performed under vacuum ata temperature of about 70° to about 250° F. for a period of timesufficient to react the desired amount of rhenium carbonyl complex withthe carrier material. In some cases an inert carrier gas such asnitrogen can be admixed with the rhenium carbonyl sublimate in order tofacilitate the intimate contacting of same with the platinum-loadedporous carrier material. A particularly preferred way of accomplishingthis rhenium carbonyl reaction step is an impregnation procedure whereinthe platinum-loaded porous carrier material is impregnated with asuitable solution containing the desired quantity of the rheniumcarbonyl complex. For purposes of the present invention, organicsolutions are preferred, although any suitable solution may be utilizedas long as it does not interact with the rhenium carbonyl complex andcause decomposition of same. Obviously, the organic solution should beanhydrous in order to avoid detrimental interaction of water with therhenium carbonyl complex. Suitable solvents are any of the commonlyavailable organic solvents such as one of the available ethers,alcohols, ketones, aldehydes, paraffins, naphthenes and aromatichydrocarbons, for example, acetone, acetyl acetone, benzaldehyde,pentane, hexane, carbon tetrachloride, methyl isopropyl ketone, benzene,n-butylether, diethyl ether, ethylene glycol, methyl isobutyl ketone,diisobutyl ketone and the like organic solvents. Best results areordinarily obtained when the solvent is acetone; consequently, thepreferred impregnation solution is rhenium carbonyl complex dissolved inanhydrous acetone. The rhenium carbonyl complex suitable for use in thepresent invention may be either the pure rhenium carbonyl itself or asubstituted rhenium carbonyl such as the rhenium carbonyl halidesincluding the chlorides, bromides, and iodides and the like substitutedrhenium carbonyl complexes. After impregnation of the carrier materialwith the rhenium carbonyl component, it is important that the solvent beremoved or evaporated from the catalyst prior to decomposition of therhenium carbonyl component by means of the hereinafter describedpyrolysis step. The reason for removal of the solvent is that I believethat the presence of organic materials such as hydrocarbons orderivatives of hydrocarbons during the rhenium carbonyl pyrolysis stepis highly detrimental to the synergistic interaction association withthe present invention. This solvent is removed by subjecting the rheniumcarbonyl impregnated carrier material to a temperature of about 100° F.to about 250° F. in the presence of an inert gas or under a vacuumcondition until substantially no further solvent is observed to come offthe impregnated material. In the preferred case where acetone is used asthe impregnation solvent, this drying of the impregnated carriermaterial typically takes about one half hour at a temperature of about225° F. under moderate vacuum conditions.

After the rhenium carbonyl component is incorporated into theplatinum-loaded porous carrier material, the resulting composite is,pursuant to the present invention, subjected to pyrolysis conditionsdesigned to decompose substantially all of the rhenium carbonylmaterial, without oxidizing either the platinum group or the decomposedrhenium carbonyl component. This step is preferably conducted in anatmosphere which is substantially inert to the rhenium carbonyl complexsuch as in a nitrogen or noble gas-containing atmosphere. Preferably,this pyrolysis step takes place in the presence of a substantially pureand dry hydrogen stream. It is of course within the scope of the presentinvention to conduct the pyrolysis step under vacuum conditions. It ismuch preferred to conduct this step in the substantial absence of freeoxygen and substances that could yield free oxygen underthe conditionsselected. Likewise, it is clear that best results are obtained when thisstep is performed in the total absence of water and of hydrocarbons andother organic materials. I have obtained best results in pyrolyzingrhenium carbonyl while using an anhydrous hydrogen stream at pyrolysisconditions including a temperature of about 300° F. to about 900° F. ormore, preferably about 400° F. to about 750° F., a gas hourly spacevelocity of about 250 to about 1500 hr.⁻¹ for a period of about 0.5 toabout 5 or more hours until no further evolution of carbon monoxide isnoted. After the rhenium carbonyl component has been pyrolyzed, it is amuch preferred practice to maintain the resulting catalytic composite inan inert environment (i.e. a nitrogen or the like inert gas blanket)until the catalyst is loaded into a reaction zone for use in thedehydrogenation of hydrocarbons.

The resulting pyrolyzed catalytic composite may, in some cases, bebeneficially subjected to a presulfiding step designed to incorporate inthe catalytic composite from about 0.01 to about 1 wt. % sulfurcalculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitabledecomposable sulfur-containing compound such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the pyrolyzed catalyst with a sulfiding gassuch as a mixture of hydrogen and hydrogen sulfide containing 1 to about10 moles of hydrogen per mole of hydrogen sulfide at conditionssufficient to effect the desired incorporation of sulfur, generallyincluding a temperature ranging from about 50° F. up to about 1000° F.It is generally a preferred practice to perform this presulfiding stepunder substantially water-free and oxygen-free conditions. It is withinthe scope of the present invention to maintain or achieve the sulfidedstate of the present catalyst during use in the dehydrogenation ofhydrocarbons by continuously or periodically adding a decomposablesulfur-containing compound, selected from the above-mentionedhereinbefore, to the reactor containing the superactive catalyst in anamount sufficient to provide about 1 to 500 wt. ppm., preferably about 1to about 20 wt. ppm. of sulfur, based on hydrocarbon charge. Accordingto another mode of operation, this sulfiding step may be accomplishedduring the pyrolysis step by utilizing a rhenium carbonyl reagent whichhas a sulfur-containing ligand or by adding H₂ S to the hydrogen streamwhich is preferably used therein.

According to the method of the present invention, the dehydrogenatablehydrocarbon is contacted with the superactive multimetallic catalyticcomposite described above in a dehydrogenation zone maintained atdehydrogenation conditions. This contacting may be accomplished by usingthe catalyst in a fixed bed system, a moving bed system, a fluidized bedsystem, or in a batch type operation; however, in view of the danger ofattrition losses of the valuable catalyst and of well-known operationaladvantages, it is preferred to use a fixed bed system. In this system,the hydrocarbon feed stream is preheated by any suitable heating meansto the desired reaction temperature and then passed into adehydrogenation zone containing a fixed bed of the catalyst previouslycharacterized. It is, of course, understood that the dehydrogenationzone may be one or more separate reactors with suitable heating meanstherebetween to insure that the desired conversion temperature ismaintained at the entrance to each reactor. It is also to be noted thatthe reactants may be contacted with the catalyst bed in either upward,downward, or radial flow fashion with the latter being preferred. Inaddition, it is to be noted that the reactants may be in the liquidphase, a mixed liquid-vapor phase, or a vapor phase when they contactthe catalyst, with best results obtained in the vapor phase.

Although hydrogen is the preferred diluent for use in the subjectdehydrogenation method, in some cases other art-recognized diluents maybe advantageously utilized, either individually or in admixture withhydrogen or each other, such as steam, methane, ethane, carbon dioxide,and the like diluents. Hydrogen is preferred because it serves thedual-function of not only lowering the partial pressure of thedehydrogentable hydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits on the catalytic composite.Ordinarily, hydrogen is utilized in amounts sufficient to insure ahydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1, with bestresults obtained in the range of about 1.5:1 to about 10:1. The hydrogenstream charged to the dehydrogenation zone will typically be recycledhydrogen obtained from the effluent stream from this zone after asuitable hydrogen separation step. As explained in my prior applicationSer. No. 833,332, a highly preferred mode of operation of the instantdehydrogenation method is in a substantially water-free environment;however, when utilizing hydrogen in the instant method, improvedselectivity results are obtained under certain limited circumstances, ifwater or a water-producing substance (such as an alcohol), ketone,ether, aldehyde, or the like oxygen-containing decomposable organiccompound) is added to the dehydrogenation zone in an amount calculatedon the basis of equivalent water, corresponding to about 1 to about5,000 wt. ppm. of the hydrocarbon charge stock, with about 1 to 1,000wt. ppm. of water giving best results. This water addition feature maybe used on a continuous or intermittent basis to regulate the activityand selectivity of the instant catalyst.

Regarding the conditions utilized in the method of the presentinvention, these are generally selected from the dehydrogenationconditions well known to those skilled in the art for the particulardehydrogenatable hydrocarbon which is charged to the process. Morespecifically, suitable conversion temperatures are selected from therange of about 700° to about 1300° F. with a value being selected fromthe lower portion of this range for the more easily dehydrogenatedhydrocarbons such as the long chain normal paraffins and from the higherportion of this range for the more difficulty dehydrogenatedhydrocarbons such as propane, butane, and the like hydrocarbons. Forexample, for the dehydrogenation of C₆ to C₃₀ normal paraffins, bestresults are ordinarly obtained at a temperature of about 800° to about950° F.; on the other hand, for the dehydrogenation of propane, bestresults are usually achieved at a temperature of about 1150° F. to 1250°F. The pressure utilized is ordinarly selected at a value which is aslow as possible consistent with the maintenance of catalyst stabilityand is usually about 0.1 to about 10 atmospheres with best resultsordinarily obtained in the range of about 0.5 to about 3 atmospheres. Inaddition, a liquid hourly space velocity (calculated on the basis of thevolume amount, as a liquid, of hydrocarbon charged to thedehydrogenation zone per hour divided by the volume of the catalyst bedutilized) is selected from the range of about 1 to about 40 hr.⁻¹, withbest results for the dehydrogenation of long-chain normal paraffinstypically obtained at a relatively high space velocity of about 20 to 35hr.⁻¹ and for the more refractory paraffins at a space velocity of about3 to about 10 hr.⁻¹.

Regardless of the details concerning the operations of thedehydrogenation step, an effluent stream will be withdrawn therefrom.This effluent will usually contain unconverted dehydrogenatablehydrocarbons, hydrogen, and products of the dehydrogenation reaction.This stream is typically cooled and passed to a hydrogen-separating zonewherein a hydrogen-rich vapor phase is allowed to separate from ahydrocarbon-rich liquid phase. In general, it is usually desired torecover the unreacted dehydrogenatable hydrocarbon from thishydrocarbon-rich liquid phase in order to make the dehydrogenationprocess economically attractive. This recovery operation can beaccomplished in any suitable manner known to the art such as by-passingthe hydrocarbon-rich liquid phase through a bed of suitable adsorbentmaterial which has the capability to selectively retain thedehydrogenated hydrocarbons contained therein or by contacting same witha solvent having a high selectivity for the dehydrogenated hydrocarbon,or by a suitable fractionation scheme where feasible. In the case wherethe dehydrogenated hydrocarbon is a mono-olefin, suitable adsorbentshaving this capability are activated silica gel, activated carbon,activated alumina, various types of specially prepared zeoliticcrystalline alumino-silicates, molecular sieves, and the likeadsorbents. In another typical case, the dehydrogenated hydrocarbons canbe separated from the unconverted dehydrogentable hydrocarbons byutilizing the inherent capability of the dehydrogenated hydrocarbons toeasily enter into several well-known chemical reactions such asalkylation, oligomerization, halogenation, sulfonation, hydration,oxidation, and the like reactions. Irrespective of how thedehydrogenated hydrocarbons are separated from the unreactedhydrocarbons, a stream containing the unreacted dehydrogenatablehydrocarbons will typically be recovered from this hydrocarbonseparation step and recycled to the dehydrogenation step. Likewise, thehydrogen phase present in the hydrogen-separating zone will be withdrawntherefrom, a portion of it vented from the system in order to remove thenet hydrogen make, and the remaining portion is typically recycledthrough suitable compressing means to the dehydrogenation step in orderto provide diluent hydrogen therefor.

In a preferred embodiment of the present invention wherein long chainnormal paraffin hydrocarbons are dehydrogenated to the correspondingnormal mono-olefins, a preferred mode of operation of this hydrocarbonrecovery step involves an alkylation reaction. In this mode, thehydrocarbon-rich liquid phase withdrawn from the hydrogen-separatingzone is combined with a stream containing an alkylatable aromatic andthe resulting mixture passed to an alkylation zone containing a suitablehighly acid catalyst such as an anhydrous solution of hydrogen fluoride.In the alkylation zone the mono-olefins react with alkylatable aromaticwhile the unconverted normal paraffins remain substantially unchanged.The effluent stream from the alkylation zone can then be easilyseparated, typically by means of a suitable fractionation system, toallow recovery of the unreacted normal paraffins. The resulting streamof unconverted normal paraffins is then usually recycled to thedehydrogenation step of the present invention.

The following working examples are introduced to illustrate further thedehydrogenation method and the superactive multimetallic catalyticcomposite of the present invention. These examples of specificembodiments of the present invention are intended to be illustrativerather than restrictive.

These examples are all performed in a laboratory scale dehydrogenationplant comprising a reactor, a hydrogen separating zone, heating means,cooling means, pumping means, compressing means, and the likeconventional equipment. In this plant, the feed stream containing thedehydrogenatable hydrocarbon is combined with a hydrogen-containing,substantially water-free, recycle gas stream and the resultant mixtureheated to the desired conversion temperature, which refers herein to thetemperature maintained at the inlet to the reactor. The heated mixtureis then passed into contact with the instant superactive multimetalliccatalyst which is maintained as a fixed bed of catalyst particles in thereactor. The pressures reported herein are recorded at the outlet fromthe reactor. An effluent stream is withdrawn from the reactor, cooled,and passed into the hydrogen-separating zone wherein ahydrogen-containing gas phase separates from a hydrocarbon-rich liquidphase containing dehydrogenated hydrocarbons, unconverteddehydrogenatable hydrocarbons, and a minor amount of side products ofthe dehydrogenation reaction. A portion of the hydrogen-containing gasphase is recovered as excess recycle gas with the remaining portionbeing continuously recycled, after water addition as needed, throughsuitable compressing means to the heating zone as described above. Thehydrocarbon-rich liquid phase from the separating zone is withdrawntherefrom and subjected to analysis to determine conversion andselectivity for the desired dehydrogenated hydrocarbon as will beindicated in the Examples. Conversion numbers of the dehydrogenatablehydrocarbon reported herein are all calculated on the basis ofdisappearance of the dehydrogenatable hydrocarbon and are expressed inmole percent. Similarly, selectivity numbers are reported on the basisof moles of desired hydrocarbon produced per 100 moles ofdehydrogenatable hydrocarbon converted.

All of the catalysts utilized in these examples are prepared accordingto the following preferred method with suitable modification instoichiometry to achieve the compositions reported in each example.First, an alumina carrier material comprising 1/16 inch spheres havingan apparent bulk density of about 0.3 g/cc is prepared by: forming analumina hydroxyl chloride sol by dissolving substantially pure aluminumpellets in a hydrochloric acid solution, adding hexamethylenetetramineto the resulting alumina sol, gelling the resulting solution by droppinit into an oil bath to form spherical particles of an alumina hydrogel,aging, and washing the resulting particles with an ammoniacal solutionand finally drying, calcining, and steaming the aged and washedparticles to form spherical particles of a substantially halogen-freegamma-alumina containing substantially less than 0.1 wt.% combinedchloride. Additional details as to this method of preparing this aluminacarrier material are given in the teachings of U.S. Pat. No. 2,620,314.

An aqueous impregnation solution containing chloroplatinic acid, nitricacid and (when an alkali or alkaline earth component is used) eitherlithium nitrate or potassium nitrate is then prepared. The aluminacarrier material is thereafter admixed with the impregnation solution.The amounts of the metallic reagents contained in this impregnationsolution are calculated to result in a final composite containing thehereinafter specified amounts of the metallic components. In order toinsure uniform dispersion of the platinum component throughout thecarrier material, the amount of nitric acid used in this impregnationsolution is about 5 wt.% of the alumina particles. This impregnationstep is performed by adding the carrier material particles to theimpregnation mixture with constant agitation. In addition, the volume ofthe solution is approximately the same as the bulk volume of the aluminacarrier material particles so that all of the particles are immersed inthe impregnation solution. The impregnation mixture is maintained incontact with the carrier material particles for a period of about 1/2 toabout 3 hours at a temperature of about 70° F. Thereafter, thetemperature of the impregnation mixture is raised to about 225° F. andthe excess solution is evaporated in a period of about 1 hour. Theresulting dried impregnated particles are then subjected to an oxidationtreatment in a dry air stream at a temperature of about 975° F. and aGHSV of about 500 hr.⁻¹ for about 1/2 hour. This oxidation step isdesigned to convert substantially all of the metallic ingredients to thecorresponding oxide forms. The resulting oxidized spheres aresubsequently contacted in a steam stripping step with an air streamcontaining about 1 to about 30% stream at a temperature of about 800° toabout 1000° F. for an additional period of about 1 to about 5 hours inorder to reduce any residual combined chloride to a value less than 0.5wt.% and most preferably less than 0.2 wt.%. The oxidized andsteam-stripped spheres are thereafter subjected to a second oxidationstep with a dry air stream at 975° F. and a GHSV of 500 hr.⁻¹ for anadditional period of about 1/2 hour.

The resulting oxidized, steam-stripped carrier material particles arethen subjected to a dry reduction treatment designed to reducesubstantially all of the platinum component to the elemental state andto maintain a uniform dispersion of this component in the carriermaterial. This reduction step is accomplished by contacting theparticles with a hydrocarbon-free, dry hydrogen stream containing lessthan 5 vol. ppm. H₂ O at a temperature of about 1050° F., a pressureslightly above atmospheric, a flow rate of hydrogen through theparticles corresponding to a GHSV of about 400 hr.⁻¹ and for a period ofabout one hour.

Rhenium carbonyl complex, Re₂ (CO)₁₀, is thereafter dissolved in ananhydrous acetone solvent in order to prepare the rhenium carbonylsolution which was used as the vehicle for reacting rhenium carbonylwith the carrier material containing the uniformly dispersed platinummetal. The amount of the complex used is selected to result in afinished catalyst containing the hereinafter specified amount ofcarbonyl-derived rhenium metal. The resulting rhenium carbonyl solutionis then contacted under appropriate impregnation conditions with thereduced, platinum-containing alumina carrier material resulting from thepreviously described reduction step. The impregnation conditionsutilized are: a contact time of about one half to about three hours, atemperature of about 70° F. and a pressure of about atmospheric. It isimportant to note that this impregnation step is conducted under anitrogen blanket so that oxygen is excluded from the environment andalso this step was performed under anhydrous conditions. Thereafter, theacetone solvent is removed under flowing nitrogen at a temperature ofabout 175° F. for a period of about one hour. The resulting dry rheniumcarbonyl impregnated particles are then subjected to a pyrolysis stepdesigned to decompose the rhenium carbonyl component. This step involvessubjecting the carbonyl impregnated particles to a flowing hydrogenstream at a first temperature of about 230° F. for about one half hourat a GHSV of about 600 hr.⁻¹ and at atmospheric pressure. Thereafter, inthe second portion of the pyrolysis step, the temperature of theimpregnated particles is raised to about 575° F. for an additionalinterval of about one hour until the evolution of CO was no longerevident. the resulting catalyst is then maintained under a nitrogenblanket until it was loaded into the reactor in the subsequentlydescribed reforming test.

EXAMPLE I

The reactor is loaded with 100 cc of a catalyst containing, on anelemental basis, 0.375 wt.% platinum, 0.375 wt.% rhenium, and less than0.15 wt.% chloride. This corresponds to an atomic ratio of rhenium toplatinum of 1.05:1. The feed stream utilized is commercial gradeisobutane containing 99.7 wt.% isobutane and 0.3 wt.% normal butane. Thefeed stream is contacted with the catalyst at a temperature of 975° F.,a pressure of 10 psig., a liquid hourly space velocity of 4.0 hr.⁻¹, anda recycle gas to hydrocarbon mole ratio of 3:1. The dehydrogenationplant is lined-out at these conditions and a 20 hour test periodcommenced. The hydrocarbon product stream from the plant is continuouslyanalyzed by GLC (gas liquid chromatography) and a high conversion ofisobutane is observed with a high selectivity for isobutylene.

EXAMPLE II

The catalyst contains, on an elemental basis, 0.375 wt.% platinum, 0.5wt.% rhenium, 0.6 wt.% lithium, and less than 0.15 wt.% combinedchloride. These amounts correspond to the following atomic ratios: Re/ptof 1.4:1 and Li/Pt of 45:1. The feed stream is commercial grade normaldodecane. The dehydrogenation reactor is operated at a temperature of850° F., a pressure of 10 psig., a liquid hourly space velocity of 32hr.⁻¹, and a recycle gas to hydrocarbon mole ratio of 5:1. After aline-out period, a 20 hour test period is performed during which theaverage conversion of the normal dodecane is maintained at a high levelwith a selectivity for normal dodecane of about 90%.

EXAMPLE III

The catalyst is the same as utilized in Example II. The feed stream isnormal tetradecane. The conditions utilized are a temperature of 830°F., a pressure of 20 psig., a liquid hourly space velocity of 32 hr.⁻¹,and a recycle gas to hydrocarbon mole ratio of 4:1. After a line-outperiod, a 20 hour test shows an average conversion of about 12%, and aselectivity for normal tetradecane of about 90%.

EXAMPLE IV

The catalyst contains, on an elemental basis, 0.2 wt.% platinum, 0.2wt.% rhenium, and 0.4 wt.% lithium, with combined chloride being lessthan 0.2 wt.%. The pertinent atomic ratios are: Re/Pt of 1.05:1 andLi/Pt of 56:1. The feed stream is substantially pure cyclohexane. Theconditions utilized are a temperature of 900° F., a pressure of 100psig., a liquid hourly space velocity of 3.0 hr.⁻¹, and a recycle gas tohydrocarbon mole ratio of 4:1. After a line-out period, a 20 hour testis performed with almost quantitative conversion of cyclohexane tobenzene and hydrogen.

EXAMPLE V

The catalyst is the same as in Example IV. The feed stream is commercialgrade ethylbenzene. The conditions utilized are a pressure of 15 psig.,a liquid hourly space velocity of 32 hr.⁻¹, a temperature of 1010° F.,and a recycle gas to hydrocarbon mole ratio of 3:1. During a 20 hourtest period, 85% or more of equilibrium conversion of the ethylbenzeneis observed. The selectivity for styrene is about 90%.

EXAMPLE VI

The catalyst contains, on an elemental basis, about 0.75 wt.% platinum,about 0.8 wt.% rhenium, about 0.6 wt.% lithium and less than 0.2 wt.%chlorine. The relevant atomic ratios are: Re/Pt of 1.12:1 and Li/Pt of22.6:1. The charge stock is substantially pure propane. The conditionsutilized are: an inlet reaction temperature of 1150° F., a pressure of10 psig., a hydrogen to propane mole ratio of 2:1 and a liquid hourlyspace velocity of about 5 hr.⁻¹. Results are: a conversion of propane ofabout 35% at a selectivity for propylene of about 85%.

It is intended to cover by the following claims all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formulation art or in the hydrocarbon dehydrogenation art.

I claim as my invention:
 1. A method for dehydrogenating adehydrogenatable hydrocarbon comprising contacting the hydrocarbon, athydrocarbon dehydrogenation conditions, with a catalytic compositeconsisting essentially of a combination of a catalytically effectiveamount of a pyrolyzed rhenium carbonyl component with a porous carriermaterial containing a uniform dispersion of a catalytically effectiveamount of a platinum group component maintained in the elementalmetallic state.
 2. A method as defined in claim 1 wherein thedehydrogenatable hydrocarbon is admixed with hydrogen when it contactsthe catalytic composite.
 3. A method as defined in claim 1 wherein theplatinum group component is platinum.
 4. A method as defined in claim 1wherein the platinum group component is iridium.
 5. A method as definedin claim 1 wherein the platinum group component is rhodium.
 6. A methodas defined in claim 1 wherein the platinum group component is palladium.7. A method as defined in claim 1 wherein the catalytic compositecontains the components in amounts, calculated on an elemental basis,corresponding to about 0.01 to about 2 wt.% platinum group metal andabout 0.01 to about 5 wt.% rhenium.
 8. A method as defined in claim 1wherein the porous carrier material is a refractory inorganic oxide. 9.A method as defined in claim 8 wherein the refractory inorganic oxide isalumina.
 10. A method as defined in claim 1 wherein the catalyticcomposite is in a substantially halogen-free state.
 11. A method asdefined in claim 1 wherein the dehydrogenatable hydrocarbon is analiphatic hydrocarbon containing 2 to 30 carbon atoms per molecule. 12.A method as defined in claim 1 wherein the dehydrogenatable hydrocarbonis a normal paraffin hydrocabon containing 3 to 30 carbon atoms permolecule.
 13. A method as defined in claim 12 wherein said normalparaffin is propane.
 14. A method as defined in claim 1 wherein thedehydrogenatable hydrocarbon is a naphthene.
 15. A method as defined inclaim 1 wherein the dehydrogenatable hydrocarbon is an alkylaromatic,the alkyl group of which contains about 2 to 6 carbon atoms.
 16. Amethod as defined in claim 2 wherein the dehydrogenation conditionsinclude a temperature of 700° to about 1200° F., a pressure of 0.1 to 10atmospheres, a LHSV of 1 to 40 hr.⁻¹, and a hydrogen to hydrocarbon moleratio of about 1:1 to about 20:1.
 17. A method as defined in claim 12wherein the dehydrogenatable hydrocarbon is a normal paraffinhydrocarbon containing about 10 to about 18 carbon atoms per molecule.